Dreamcast Internal VGA Queries and Problems

[Link83]

Hi everyone,

I am currently trying to add an internal VGA port to my Dreamcast, but am having a few problems 

Firstly, a quick query - one of the main reasons I want to add a VGA port is so that I can have RGB Scart and VGA connected up to my Dreamcast at the same time (For the few games that dont work over VGA) None of the external VGA boxes I have seen support this (Only Composite and S-Video ports) so the only solution I could see was to add an internal VGA port.

However, I was wondering - if I were to leave RGB Scart and VGA connected up to an LCD TV at the same time - would switching the Dreamcast to VGA mode cause any problems? I would think that the Dreamcast would try and ouput a 31khz RGB signal over the Scart socket aswell as the VGA socket, so could this damage the TV? 

On to the main problem. I have just tried to add the VGA port as shown in this guide:-
http://www.mmmonkey.co.uk/console/sega/dc-vga.htm

I followed it to the letter, and have checked, double checked and triple checked all my connections and I just cant figure out was is wrong. When I try to connect it up to my LCD monitor it says 'no signal' and just turns into standby mode 

The Dreamcast is fine and still works through RGB scart - the headphone socket I added also works fine.

Unfortunately I currently dont have any other Monitor or TV I can test it out on 

So what im wondering is - are there any other pins that should be connected up in order for the monitor to detect a VGA signal?

I have been looking at VGA ports over at Wikipedia:-
http://en.wikipedia.org/wiki/VGA_connector
VGA Pic:-

How mine is wired up (Black dots are ground):-


...and was wondering if the +5v line (Pin 9) not being connected could be the problem?

Other than that I have read elsewhere that Pins 4 and 11 sometimes need to be grounded aswell - could this work and make the monitor detect the signal?

Also, some VGA switches/boxes have a 'half way' mode between switching from TV to VGA to help force some games bootin VGA - how does does this work?

Lastly, the official Dreamcast Scart cable has Pin 7 connectd to ground, but I have also read that some of the third party Scart Cables have Pin 6 connected to ground, and indeed on reading the GamesX Wiki it says there are two different 15khz RGB modes. My question is, why did Sega do this? and are they are any games that work in one but not the other? Found a thread with abit of info here:-
http://nfggames.com/forum2/index.php?topic=2504.0
but still dont fully understand it.

Phew! Thanks in advance for any help 

[kendrick]

Regarding the halfway mode, some games detect whether or not you're running in RGB/VGA mode and won't output video. The trick is to have the switch in composite output mode until you've booted the game past a certain point, after which it's safe to switch back to RGB mode. It doesn't work reliably with all games, unfortunately.

The Dreamcast puts out 640x480, so is it possible that your display just won't accept that low resolution image? Check your LCD panel specs, or alternately just pick up a cheap VGA tube at the local computer repair outfit. Most of the old tube monitors will accept that signal, and it wouldn't hurt to have one lying around for testing.

[Link83]

Thanks for your reply. My monitor definitely supports 640x480 as I have displayed that resolution before with no problems. I am hoping to get hold of an old CRT sometime soon, but even if I did and it worked correctly it wouldnt do me much good as I need it to display on this LCD monitor 

Im thinking of just going and buying a Dreamcast VGA box, and testing my monitor with that, then if it still doesnt work I can be sure its the monitor.

Unfortunately I would still be stuck in the same situation!

Any idea what it could be that my monitor is looking for to detect a signal?

[kendrick]

Re-reading your post, I see that you've left the five volt line disconnected. Not all monitors require that voltage to be present in order to accept the signal, but some might actively refuse to process video if it's not there, just as a standard safety function. It's worth connecting the 5V+ line for testing purposes, just to eliminate that as a failure point.

[NeWmAn]

However, I was wondering - if I were to leave RGB Scart and VGA connected up to an LCD TV at the same time - would switching the Dreamcast to VGA mode cause any problems? I would think that the Dreamcast would try and ouput a 31khz RGB signal over the Scart socket aswell as the VGA socket, so could this damage the TV? 

You can't get VGA via the SCART because the composite sync will not do 31KHz.

Have you got Pin #6 on the DC AV connector connected to GND?

[Link83]

However, I was wondering - if I were to leave RGB Scart and VGA connected up to an LCD TV at the same time - would switching the Dreamcast to VGA mode cause any problems? I would think that the Dreamcast would try and ouput a 31khz RGB signal over the Scart socket aswell as the VGA socket, so could this damage the TV? 

You can't get VGA via the SCART because the composite sync will not do 31KHz.

Have you got Pin #6 on the DC AV connector connected to GND?

Thanks, so there is no chance the 31khz VGA signal could be passed down the Scart cable aswell, and damage the TV's Scart socket?
When I read the guide it says:-
"I did alter it a bit as when I plugged in an RGB lead it also grounded Pin 6 on the DC motherboard which then enabled VGA mode again and caused my TV some problems!  So instead of linking pins 6 and 7 and then grouding them, I kept them seperate and grounded them individually (still using a single switch - a double pole, double throw switch)."
But he doesnt mention what these 'problems' were, or if they could be damaging to the TV?

I just want to be sure before I connect both the VGA and RGB Scart cable to a friends LCD TV

Also, I just tried connected +5v to Pin 9, but it made no difference 
I also tried connecting Pins 4 & 11 to ground and that made no difference either

I really need to get hold of an old CRT to test the VGA mod is working in the first place.
Any other suggestions for me to try in the mean time?

[NeWmAn]

Thanks, so there is no chance the 31khz VGA signal could be passed down the Scart cable aswell, and damage the TV's Scart socket?

The R,G,B lines will have the high res signal but unless you use the separate H & V lines you won't be able to display it.
I can't tell what will happen to your (your friends) TV, being a LCD (so fairly recent) I guess it will only display a blue screen and do nothing else.

Any other suggestions for me to try in the mean time?

Post some pictures of your wiring?

[Link83]

Thanks, so there is no chance the 31khz VGA signal could be passed down the Scart cable aswell, and damage the TV's Scart socket?

The R,G,B lines will have the high res signal but unless you use the separate H & V lines you won't be able to display it.
I can't tell what will happen to your (your friends) TV, being a LCD (so fairly recent) I guess it will only display a blue screen and do nothing else.

Any other suggestions for me to try in the mean time?

Post some pictures of your wiring?

Thanks for your reply. My main concern is that the 31khz VGA signal could damage the TV or Scart socket if it is still being sent down the Scart cable aswell.

Here are some pictures of my mod, I know my soldering isnt the best but it should still be working fine:-



This is the second Dreamcast I have tried it on - hence the missing Headphone cable I mentioned previously.

You can also see that I connected up the +5v line to Pin 9 with no success.

I also grounded pins 4 and 11 aswell, but it is difficult to make it out in the picture.

Any help or suggestions much appreciated 

[albino_vulpix]

Not sure if I'm seeing it right, but on your switch, only the white wire makes contact with the purple wire. If this is true, bridge the connection between the 2 middle contacts on your switch.

[Link83]

Not sure if I'm seeing it right, but on your switch, only the white wire makes contact with the purple wire. If this is true, bridge the connection between the 2 middle contacts on your switch.

There is actually a cut off resistor leg bridging the two ground points (middle points), but is isnt very clear in that picture - sorry.

[NeWmAn]

I cannot see any errors in your work, and your soldering is better than mine
I can't really tell the colors of the wires that go to the switch or the resistor bands and where's the anode of one of the diodes, but I guess that you have checked those.

I just wanted to add that you made me want to check how my DC with internal VGA is wired,  and I found that I haven't that many parts: just 2*150 Ohm resistors on the H & V wires (no capacitors, no  pullup resistors or diodes) and it has always worked with any monitor I've tried.

[Link83]

I cannot see any errors in your work, and your soldering is better than mine
I can't really tell the colors of the wires that go to the switch or the resistor bands and where's the anode of one of the diodes, but I guess that you have checked those.

I just wanted to add that you made me want to check how my DC with internal VGA is wired,  and I found that I haven't that many parts: just 2*150 Ohm resistors on the H & V wires (no capacitors, no  pullup resistors or diodes) and it has always worked with any monitor I've tried.

Abit belated I know - but many thanks for your advice and your compliment 

I gave up on this mod for a while, but just decided to take another look at it today, and I have now found out what the problem is!

I followed mmmonkeys veroboard layout 'to the letter', so couldnt understand why it wasnt working  After a closer look I noticed that the original veroboard layout is incorrect!  (I hope he doesnt mind me pointing this out)
Heres the original (incorrect) layout I followed:-


- Firstly the 4k7 and 150 ohm resistor labeling is swapped around (the 150ohms are shown as orange and the 4k7 as purple, but it should be visa-versa)
- Either the whole circuit needs to be 'flipped', or the 'VGA Socket' and' DC Motherboard'  headers need to be swapped around, as the 150ohm resistors should be the first components on the H and V sync lines.
- Lastly, depending on how the picture is changed the polarity direction of the capacitors may need to be altered so that the negative leg always faces towards the 'VGA Socket'

I should have really noticed this to begin with, but I didnt really look at the VGA circuit picture - just the veroboard layout picture.

I have edited the veroboard layout myself (with paint) so that it now follows the VGA circuit layout picture, so heres how I guess it should look (I decided to flip the circuit):-


Unfortunately even after I switched the circuit board out for another one (which followed the correct method) my Dreamcast no longer had any video output at all - even with Composite/RGB Scart. I think the motherboard/video output must have been fried from all my attempts ....but at least I can re-use the GD-Rom unit 

I tested the new circuit board I had made on another Dreamcast and it worked perfectly first time 

I will email mmmonkey to let him know about the errors - I hope he isnt offended. His site has always been an excellent source for guides (aswell as gamesx of course!) and if it hadnt been for his site I dont think I would have ever had the courage to start modding to begin with

[NeWmAn]

Good Job!
BTW, if you are going to permanently install the VGA socket to the DC you could ditch the switch:  just use some of the unused GND pins to activate the selection.
Edit: Mmmh Just seen that it was already written on mmmonkey's site: "I think it would be possible to do with without a switch by utilising the ground points on the VGA socket and linking them up to AV pins 6 and 7 (instead of linking the VGA ground pins together)."

I wanted also show you where I got the H & V sync on my DC: